Geochronology and Geochemistry of Ore-Hosting Rhyolitic Tuff in the Kengdenongshe Polymetallic Deposit in the Eastern Segment of the East Kunlun Orogen

The Kengdenongshe Au-Ag-Pb-Zn polymetallic deposit, a newly discovered large-scale polymetallic deposit in the southeastern section of the East Kunlun Orogen (EKO), contains an Au resource of 40 t, Ag resource of 690 t and Pb-Zn resource of 10.5 x 10(5) t. The ore-bearing rocks are mainly composed of laminar barite and rhyolitic tuff. In this study, LA-ICP-MS zircon U-Pb dating and whole rock major and trace elements analyses have been conducted on the ore-bearing rhyolitic tuff. LA-ICP-MS zircon U-Pb dating data show that these rhyolitic tuffs were emplaced at ca. 243.3 +/- 1.6 Ma. The samples show similar features to those of S-type granites, including high contents of SiO2 (76.4-82.6 wt. %) and Al2O3 (11.0-12.7 wt. %) and relatively low concentrations of Na2O (0.35-2.43 wt. %) and CaO (0.095-0.124 wt. %), with high A/CNK (molar [Al2O3/(CaO + Na2O + K2O)]) (1.72-2.03) and K2O/Na2O ratios (1.41-17.1). Further, they exhibit depletion in HFSEs (High Field Strength Elements) and enrichment in LREEs (Light Rare Earth Element) with negative Eu anomalies (Eu/Eu* = 0.51-0.64). These geochemical characteristics indicate that the Kengdenongcuo rhyolitic tuff originated from the fluid-absent melting of a plagioclase-poor, clay-rich metapelitic source and experienced minor fractional crystallization. In combination with arc-type magmatism and contemporaneous syn-collision granitoids in the region, the Kengdenongcuo tuff formed in a continental collision setting, implying that the Bayan Har-Songpan Ganzi Terrane collided with the East Kunlun Terrane and the Paleo-Tethys Ocean was closed at the period of similar to 243 Ma. The Kengdenongcuo polymetallic deposit formed at about the same time.